The present invention relates to multiple integrated laser engagement system (MILES), and in particular to a system for and a method of encoding a MILES code word to convey a significantly increased amount of information.
MILES has revolutionized the manner in which armies train for combat, and has become the standard against which all other tactical engagement simulation (TES) systems are measured. It is highly valued for its ability to accurately assess battle outcomes and to teach soldiers the skills required to survive in combat and destroy an enemy. With MILES, commanders at all levels can conduct opposing force free-play tactical engagement simulation training exercises that duplicate the lethality and stress of actual combat.
The MILES system uses laser bullets to simulate the lethality and realism of a modern tactical battlefield. Laser transmitters, capable of shooting pulses of encoded infrared energy, simulate the effects of live ammunition. The transmitters are easily attached to and removed from hand-carried and vehicle mounted direct fire weapons. Detectors located on opposing force troops and vehicles receive the coded laser pulses. MILES decoders then determine whether a weapon that could cause damage to the target hit the target and whether the laser bullet was accurate enough to cause a casualty. The target vehicles or troops are made instantly aware of the accuracy of the shot by means of audio alarms and visual displays, which can indicate either a hit or a near miss.
Detectors located on a target receive the encoded infrared energy transmitted upon firing a weapon. In the case of ground troops, the detectors are normally installed on webbing material that resembles a standard-issue load-carrying lift harness. Additional detectors may be attached to a web band that fits on standard-issue helmets. For vehicles, the detectors are mounted on belts that attach to the front, rear, and sides of the vehicles. The detectors provide 360xc2x0 coverage in azimuth and sufficient elevation coverage to receive the infrared energy during an air attack. The arriving pulses that are sensed by detectors are amplified and compared to a threshold level. If the pulses exceed the threshold, that information is registered in detection logic. Once a proper arrangement of information exists, corresponding to a valid code for a particular weapon, the decoder decides whether the code is a near miss or a hit. If a hit is registered, a hierarchy decision is then made to determine if the specific weapon can indeed cause a kill against the particular target and, if so, what the probability of a kill might be.
Because MILES is a pulse-code-modulation optical communication system in which the transmission medium is the atmosphere, the encoded message is inherently transmitted through and affected by varying atmospheric conditions. When received, the encoded message is decoded to initiate required actions. Ideally, the message as decoded accurately represents weapon firing characteristics, round dispersion patterns, and the probability of hit as a function of range for specific weapon systems.
The standard defining the MILES code structure contains weapon codes and player identification (PID) codes embedded in it. The present MILES code word structure does not allow the transmission of any additional information, due to pulse timing constraints. In consequence, only a limited amount of information can be encoded and transmitted, which reduces the fidelity of casualty assessments and provides an inadequate after-action-review.
The MILES system is based on the receiving system receiving an encoded laser word. Each unique weapon system is fitted with a laser transmitter to match its weapon characteristics. The energy of the laser transmitter is preset to match the weapon system characteristics for a given laser detection system sensitivity and atmospheric conditions. Thus, the energy of the laser transmitter and the sensitivity of the detection system have to be properly set and maintained to accurately simulate the effect a weapon would have on a target. The negative effects of atmospheric attenuation (e.g., continuum atmospheric attenuation, water vapor attenuation, and scintillation) are accepted as inherent limitations to the fidelity of the MILES system.
It would be desirable to improve the MILES system to enable transmission of additional information (e.g. GPS position/location, range, elevation, lead angle, impact point of a projectile, etc.). This would greatly enhance the fidelity of hits and casualty assessments. This additional information would also provide for a vastly enhanced after action review, and enable a soldier to better train for future missions. Further, the transmission of GPS position/location would eliminate the need to carefully set and maintain the energy and sensitivity of associated laser transmitter and detection systems.
Known laser based tactical engagement simulation training systems are disclosed by U.S. Pat. Nos. 4,629,427, 4,662,845 and 4,823,401, the teachings of which are specifically incorporated herein by reference.
An object of the present invention is to provide an improved laser based tactical engagement simulation training system.
Another object is to provide an improved MILES system that enables the transmission of an increased amount of information in a MILES code word.
A further object is to provide such a MILES system in which individual bits of information in a standard encoded MILES word are modulated to contain additional information.
Still another object is to provide such a MILES system in which the bits of information in the standard MILES code word are FM modulated.
Yet another object is to provide such a system that is downward compatible with a standard MILES system.
In accordance with the present invention, there is provided an improved MILES code word structure in which FM modulated pulses of selected frequencies occur in the same positions in the code word as would individual bits of logic level xe2x80x9c1xe2x80x9d in a standard MILES code word. In the improved MILES code word, each selected frequency is assigned a value unique to it, and an FM modulated bit in a predetermined position in the code word has a frequency indicative of information conveyed by the remaining FM modulated bits of the same code word. Each FM modulated bit comprises at least two pulses at a selected frequency occurring during the same time frame as would the logic xe2x80x9c1xe2x80x9d bit of the standard MILES code word, and the frequency of each the FM modulated bit is determined according to the formula f=1/t, where t is the time interval between leading edges of two successive pulses of individual ones of the FM modulated bits.
There also is provided an improved MILES system. The system comprises means for generating a MILES code word having a standard MILES code word structure in which a predetermined number of bits are logic level xe2x80x9c1xe2x80x9d and are in bit positions selected to convey standard required information, and in which the remaining bits are logic level xe2x80x9c0xe2x80x9d. Means are included for FM modulating to selected frequencies individual ones of the logic level xe2x80x9c1xe2x80x9d bits of the standard MILES code word, and each selected frequency has an assigned value, so that the FM modulated MILES code word contains both the standard required information and information in addition to the standard required information.
The improved MILES system advantageously includes means for controlling operation of a laser to generate and transmit a pulsed laser signal representative of the FM modulated MILES code word. There are means for receiving and decoding the pulsed laser signal to obtain therefrom at least the standard required information contained in the FM modulated MILES code word, and preferably both the standard required information and the additional information. A predetermined one of the FM modulated bits of the code word has a frequency indicative of the nature of the information conveyed by the remaining FM modulated bits of the same code word, and advantageously the predetermined one of the FM modulated bits is the first FM modulated bit of the code word. Each FM modulated bit comprises at least two pulses at a selected frequency and occurring during the same time frame as the original logic xe2x80x9c1xe2x80x9d bit, and the frequency of each is determined according to the formula f=1/t, where t is the time interval between leading edges of two successive pulses of the FM modulated bit.
The means for controlling operation of the laser includes a laser driver that provides constant power or energy to the laser for each pulse output by the laser. The means for receiving and decoding the pulsed laser signal includes a detector for receiving and generating an amplified representation of the received pulsed laser signal, and means for generating a signal representative of occurrence of a logic xe2x80x9c1xe2x80x9d bit in response to occurrence of either an FM modulated logic xe2x80x9c1xe2x80x9d bit or a logic xe2x80x9c1xe2x80x9d bit of a standard MILES code word.
The invention also provides a method of generating an improved code word for a laser based tactical engagement simulation training system of a type in which a standard code word for the system consists of a plurality of bits of logic level xe2x80x9c1xe2x80x9d in selected positions in the code word, with the remainder of the bits being of logic level xe2x80x9c0xe2x80x9d. The method comprises the steps of providing a standard code word, and FM modulating to selected frequencies individual logic level xe2x80x9c1xe2x80x9d bits of the standard code word.
Advantageously, each selected frequency is assigned a value unique to it, and a logic level xe2x80x9c1xe2x80x9d bit in a predetermined position in the standard code word is FM modulated to have a frequency indicative of information conveyed by the remaining FM modulated bits of the same standard code word. FM modulating causes at least two pulses at a selected frequency to occur during the same time frame as a logic xe2x80x9c1xe2x80x9d bit, and the frequency to which logic xe2x80x9c1xe2x80x9d bits are modulated is controlled according to the formula f=1/t, where t is the time interval between leading edges of two successive pulses of individual ones of the FM modulated bits.
In the described embodiment the method generates an improved MILES code word, and comprises the step of modifying individual ones of the logic level xe2x80x9c1xe2x80x9d bits of a standard MILES code word to contain information in addition to the information required to be contained in the standard MILES code word. The modifying step may comprise embedding into individual ones of the logic level xe2x80x9c1xe2x80x9d bits of the standard MILES code word information in addition to the information required to be contained in the standard MILES code word, and in the described embodiment comprises FM modulating individual ones of the logic level xe2x80x9c1xe2x80x9d bits. The FM modulating step includes modulating the logic level xe2x80x9c1xe2x80x9d bits to have selected frequencies, and to each selected frequency is assigned a value unique to it. Also, logic level xe2x80x9c1xe2x80x9d bit in a predetermined position in the standard code word is FM modulated to have a frequency indicative of information conveyed by the remaining FM modulated bits of the same code word, and FM modulating causes at least two pulses at a selected frequency to occur during the same time frame as a logic xe2x80x9c1xe2x80x9d bit. The frequency to which logic xe2x80x9c1xe2x80x9d bits are modulated is controlled according to the formula f=1/t, where t is the time interval between leading edges of two successive pulses of individual ones of the FM modulated bits.
The invention further contemplates a method of operating a MILES system, comprising the steps of generating a MILES code word having a standard MILES code word structure in which a predetermined number of bits are logic level xe2x80x9c1xe2x80x9d and are in bit positions selected to convey standard required information, and in which the remaining bits are logic level xe2x80x9c0xe2x80x9d; modifying individual logic level xe2x80x9c1xe2x80x9d bits of the standard MILES code word to contain information in addition to the required information; and controlling operation of a laser in response to the modified code word to generate and transmit a pulsed laser signal representative of the modified code word. The modifying step may comprises embedding the additional information into individual ones of the logic level xe2x80x9c1xe2x80x9d bits of the standard MILES code word, although as described it comprises FM modulating individual ones of the logic level xe2x80x9c1xe2x80x9d bits.
Included in the method of operating the system is receiving and decoding the pulsed laser signal to obtain therefrom at least the standard required information contained in the modified code word, and advantageously both the standard required information and the additional information. Further, a predetermined one of the logic xe2x80x9c1xe2x80x9d bits is modified to contain information identifying the nature of the information conveyed by the remaining modified bits of the same code word, and the predetermined bit advantageously is the first logic xe2x80x9c1xe2x80x9d bit of the MILES code word.
Each FM modulated bit comprises at least two pulses at a selected frequency and occurring during the same time frame as the original logic xe2x80x9c1xe2x80x9d bit, and the FM modulating step is performed so that the frequency of each FM modulated bit is determined according to the formula f=1/t, where t is the time interval between leading edges of two successive pulses of the FM modulated bit. Controlling operation of the laser operates a laser driver to provide constant power or energy to the laser for each modified logic xe2x80x9c1xe2x80x9d bit to be output by the laser.
The foregoing and other objects, advantages and features of the invention will become apparent upon a consideration of the following detailed description, when taken in conjunction with the accompanying drawings.